Date: Wed, 30 Dec 1998 20:00:22 -0500 From: Christian Kuhtz <ck@ns1.adsu.bellsouth.com> To: Gary Palmer <gpalmer@FreeBSD.ORG> Cc: "Steven P. Donegan" <donegan@quick.net>, Mike Smith <mike@smith.net.au>, Josh Tiefenbach <josh@ican.net>, The Hermit Hacker <scrappy@hub.org>, freebsd-current@FreeBSD.ORG Subject: Re: NOW/MOSIX/Beowulf Message-ID: <19981230200022.K828@ns1.adsu.bellsouth.com> In-Reply-To: <29073.915064796@gjp.erols.com>; from Gary Palmer on Wed, Dec 30, 1998 at 07:39:56PM -0500 References: <28977.915064476@gjp.erols.com> <29073.915064796@gjp.erols.com>
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On Wed, Dec 30, 1998 at 07:39:56PM -0500, Gary Palmer wrote:
> > Sharing LDAP caches like that doesn't work.
>
> Whoops. Guess I should say a bit more about *why* shouldn't I?
>
> If you think about it, each LDAP `replica' (even if they share the same DBM
> backend over NFS, and you could find an LDAP server which supported read-only
> operation like that), you still could run into troubles. Since each replica
> has in-core state about the file, have differet replicas write different
> updates to different parts of the file could lead to some interesting results
> ... even with good file/record locking, I think that is a path full of risk.
Gary is very much correct. That is why most vendors didn't want the IETF to
implement multimaster, because their backend databases couldn't handle complex
state maintenance (particularly Netscape's Berkeley DB based implementation).
So, time to market was gained by sacrificing architecture, yielding a cute but
unusable architecture for large scale deployment. A lot of the vendors use a
Berkeley db (cute, but not really what we need) or an RDBMS (yuck).
Directories are object databases, which is different from DB(M) or RDBMS. And
also the reason why most implementations based on the latter suck. ;^)
So, multimaster is tricky, unless you're running another multimaster directory
technology underneath and LDAP becomes little more than an 'API'. Nothing
wrong with that, I might add.
Cheers,
Chris
--
Frisbeetarianism, n.:
The belief that when you die, your soul goes up on the roof and gets stuck.
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